By Carolyn Gramling, staff writer for Science and editor of the In Brief section.

NASA's Scientific Visualization Studio/Cindy Starr.Antarctic
sea ice extent reached a record high this year on 22 September, topping 20
million square kilometers for the first time since 1979, according to the
National Snow and Ice Data Center. (Average maximum extent from 1979 to 2014 is
in red.)

And as scientists have begun to look more closely at what’s
happening around Antarctica, one point stands out: While there is a net gain,
that gain is actually the sum of even stronger increases and decreases in sea
ice extent at different locations around the continent. Some places, like the
Ross Sea, have seen growth of sea ice—but others, like the Bellingshausen Sea
west of the Antarctic Peninsula, have seen significant sea ice loss. That could
mean that changing wind patterns are sweeping warm air over some parts of the
continent and cold air over others—which may in
turn be influenced by the ozone hole in the atmosphere.

Q: Why did Antarctic sea ice hit a record high this year?

A: NSIDC notes a couple of possible factors.
One, again, is changing wind patterns; in July, NSIDC noted that a strong-low
pressure pattern over the Amundsen Sea during June had brought lower-than-usual
temperatures. Another possible contribution is actually related to melting—of
the continental ice sheet. Deep ocean water, which is relatively warm, has been
melting portions of the ice sheet at its base. When that cold, fresh water
enters the ocean, it
forms an extra-chilly layer on the ocean surface around the continent.
That’s another condition that favors sea ice growth. And, as Walt Meier of
NASA’s Goddard Space Flight Center noted here,
Antarctic sea ice already covers a huge area—it doesn’t take much growth for it
to set a new record.

"What we're learning is, we have more to learn,"
said Ted Scambos, lead scientist at NSIDC, in the agency’s press release this
week.